Santa Claus Suit In May (Syndrome) is a term for when someone keeps acting a certain way even though they have grown up or the situation changes and they should not still be acting that way. Usualy, it is very disturbing.
I coined the term after Bill Doutrive(sp?) in the show "King Of the Hill" continued to wear a Santa Claus suit long after the holidays because he did not want to let go of the good times and contentment he had that year. The suit decayed and became very smelly and soiled and his "holidayland" he had set up in his yard was overrun by beer drinking punks. This was no doubt disturbing.
A person acting and dressing like they are in middle school even though they are 40 years old
"I can't stand her. She has a terrible case of SCSIM!"
A bride continuing to wear her wedding dress a week after the groom left her at the altar.